Keen
<p>
Fill in the grid with digits from 1 to the grid size, so that every
digit appears exactly once in each row and column, and so that all
the arithmetic clues are satisfied (i.e. the clue number in each
thick box should be possible to construct from the digits in the box
using the specified arithmetic operation).
<p>
To place a number, click in a square to select it, then type the
number on the keyboard. To erase a number, click to select a square
and then press Backspace.
<p>
Right-click in a square and then type a number to add or remove the
number as a pencil mark, indicating numbers that you think
<em>might</em> go in that square.
